I needed few months back to make a fixed-length ID iut if none-fixed-length numbers.
SO I used the function REPT with RIGHT to force all numbers to be converted into fixed-length ID (mainly having leading zeros)
And here is the formula
=Right(Rept("0", 12)&J5, 12)
J5 is where the ID can be found
12 is the length of the ID we wanted